This invention relates to printing generally, and is more specifically directed to a process of printing and transferring an image to a final substrate.
The use of computer technology allows substantially instantaneous printing of images. For example, video cameras or scanners may be used to capture a color image on a computer. The image may then be printed onto substrates from the computer by any suitable printing means capable of printing in multiple colors, including mechanical thermal printers, ink jet printers and electrophotographic or electrostatic printers. These printing technologies are widely practiced and well understood. The methods for making full color inks and toners are also well documented. The substrates for these conventional applications, however, are limited to those that the printers can handle, invariably, smooth metal, plastic or papers of limited thickness.
Techniques are well known in the art for printing onto clothing, other textile materials, and other objects, such as wood, plastics, glass and ceramics including silk screening, digitally produced sublimation transfers, and mechanically bonded thermal transfers.
Conventional heat-melt thermal printing uses primarily non-active wax or wax-like materials such as hydrocarbon wax, carnauba wax, ester wax, paraffin wax, hot-melt resin, thermoplastic, or polymeric materials, etc. as heat-melt material. The resulting image has poor permanency since the conventional wax materials are not chemically bonded or otherwise permanently grafted to the substrate, but are temporarily and loosely bound to the final substrate by the melting of wax materials during the transfer process. The resulting image is not durable, with the wax materials being washed away during laundering of textile substrates on which the image is transferred, along with the dyes or colorants that form the image in the thermal ink layer.
The natural tendency of cotton fiber to absorb inks causes an image to lose its resolution and become distorted. Liquid inks other than sublimation inks wick, or are absorbed by, cotton or other absorbent substrates, resulting in printed designs of inferior visual quality, since the printed colors are not properly registered on the substrate. This is especially true when aqueous based ink paste is used for coating and fixing purposes as disclosed in Reiff, et al., U.S. Pat. No. 5,607,482. The substrates can be surface pre-coated or treated to improve the quality of images transferred onto substrates having a cotton component or other absorbent component with materials such as the coatings described in DeVries et al., U.S. Pat. No. 4,021,591. Application of polymer surface coating materials to the substrate allows the surface coating material to bond the ink layer to the substrate, reducing the absorbency of the ink by the cotton and improving the image quality. However, the gross surface coating on the substrate extends from the margins of the image after the image is applied to the substrate, which can be seen with the naked eye and adds hand to the fabric. Again the excess surface coating reduces the aesthetic quality of the printed image on the substrate. Further, the surface coating tends to turn yellow with age, which is undesirable on white and other light colored substrates. Yellowing is accelerated with laundering and other exposure to heat, chemicals or sunlight. A method described in Hale, et al. in U.S. Pat. No. 5,431,501 reduces the hand by printing a surface preparation material over the entire image, on the intermediate substrate, but not beyond the boundaries of the image. The image is then transferred from the medium to the final substrate by applying heat and pressure such that the surface preparation material permanently grafts the ink solids to the substrate.
Heat activated, or sublimation, transfer dye solids change to a gas at about 400xc2x0 F., and have a high affinity for polyester at the activation temperature. Once the gasification bonding takes place, the ink is permanently printed and highly resistant to change or fading caused by laundry products. While sublimation dyes yield excellent results when a polyester substrate is used, these dyes have a limited affinity for other materials, such as natural fabrics like cotton and wool. Accordingly, images produced by heat activated inks comprising sublimation dyes, which are transferred onto textile materials having a cotton component, do not yield the high quality images experienced when images formed by such inks are printed onto a polyester substrate. Images which are printed using sublimation dyes applied by heat and pressure onto substrates of cotton or cotton and polyester blends yield relatively poor results.
Thermal transfer sheets are known in the art and are designed for printing by various printing mechanisms. With these thermal transfer sheets, the entire sheet is transferred to the final substrate: the imaged area as well as the non-imaged area. The thus transferred material can be seen and felt in the non-imaged area. In addition, laundering and normal wear will cause the transfer material to yellow. This yellowing is obvious in the non-imaged areas, particularly against a white background, such as a t-shirt. In addition to yellowing, redeposition of colorant is often seen in the non-imaged area of the transfer film after laundering. Most commercially available heat transfer paper suppliers recommend cutting away the unprinted area of the paper prior to heat transfer. This is especially tedious and impractical when the image contains text or other fine details that must be cut around.
Transfer papers with good receptivity for images printed with wax-based inks and crayons have been disclosed. For example, a basesheet may be coated with a layer of Singapore Dammar resin for good wax-based ink receptivity.
Kronzer, U.S. Pat. No. 6,200,668 describes a transfer sheet for inkjet printing. A multi-layered sheet is formed with a basesheet of film or cellulosic nonwoven web, followed by various laminating layers. After an image is printed onto the sheet, the image-bearing laminating layers are transferred by the application of heat and pressure to the backside of the basesheet. The basesheet is desirably split from the laminating layers after the basesheet has cooled.
Bodager, et al., U.S. Pat. No. 5,984,467 describe an inkjet media composed of various layers including an ink-receiving layer, which may be transferred as a laminate to a final substrate. The ink receiving laminate is composed of about 80% adhesive, such as polyester resins, polyvinyl alcohol homopolymers and copolymers, polyvinylpyrolidone, and blends, copolymers of vinyl acetate with ethylene and/or vinyl chloride; and thermoplastic polymer and/or reactive components. Water from the inkjet ink is absorbed into an underlying water-absorbing layer composed of a hydrophilic polymer. During the lamination step the water-absorbing layer is split from the ink-receiving layer.
In the case of heat transfer sheets to be imaged by laser printers or color copiers, for example, the transfer material must have a melt point higher than the fuser rollers within the copier or printer. An image-receptive layer may be comprised of a thermoplastic polymer selected from a group comprising polyolefins, polyesters, and ethylene-vinyl acetate copolymers which melt above 100xc2x0 C.
There are a large number of patents related to thermal transfer sheets. These are distinguished from the current invention in that they generally refer to color, wax-based ink ribbon technology, and the transfer of this ink from the ribbon to a substrate via a thermal print head of elevated temperature contacting with the backside of the ribbon to melt and release the ink layer.
The use of radiation curing technology has been used in combination with transfer sheets. For example, Berqqren, et al., U.S. Pat. No. 4,291,114, produce an image by exposing a colored, photopolymerizable material of a transfer sheet to activating radiation in an image-wise manner. The image is then transferred to a substrate by the application of pressure to the backside of the transfer sheet. Bennett, et al., in U.S. Pat. No. 4,454,179 employ a radiation cure adhesive on a transfer sheet. A transparent carrier film is coated with an ink layer via conventional means, such as screen-printing. Conventional coating or laminating techniques cover the carrier film with an ink layer and then apply a radiation cured adhesive layer. After drying the adhesive layer, a release liner is applied for protective purposes. The transfer sheet is then exposed to actinic radiation through the transparent carrier film, thus curing the adhesive in the non-inked areas. The release liner is then removed and the transfer sheet is positioned on a substrate, and pressure is applied across the carrier film. The carrier film is then removed, taking the exposed adhesive with it, and leaving the ink, and underlying unexposed adhesive, bonded to the substrate.
In application Ser. No. 09/670,674 a method of transfer printing by digitally printing onto a radiation curable coated media, followed by exposing the printed media to actinic radiation, is disclosed. The exposed, non-imaged area is effectively cured and rendered non-transferable, while the image area and underlying unexposed coating are transferred to a final substrate.
Radiation curable inks are well known in the art. For example, the screen-printed inks employed in Bennett may be UV curable. Of particular interest to the present invention are radiation curable inkjet inks. Examples of such are disclosed in Caiger, eta al., U.S. Pat. No. 6,114,406, Roth, U.S. Pat. No. 5,889,084, Mantell, et al., U.S. Pat. No. 5,641,346 and Figov, U.S. Pat. No. 5,623,001, and are incorporated herein by reference.
The present invention is a process for printing and transferring an image to a final substrate. In this invention, only the imaged area is transferred and permanently fixed to a final substrate, while the non-imaged area is processed to have little or no affinity for the final substrate, and is not bound to the final substrate.
A receiver sheet comprises a thermally transferable film. The receiver sheet is imaged, such as by printing the film with any ink or toner. The receiver sheet is either separately or simultaneously applied with a radiation curable material in the non-imaged area. As a result, part of the film is covered by the image, and the remainder is covered with the radiation curable material that is printed or applied in the non-imaged area. After printing, the radiation curable material is cured by exposing the sheet to a radiation source.
The sheet is then placed in contact with a final substrate, such as a t-shirt, with the ink side in contact with the substrate, and energy (e.g., heat) is applied to the back of the receiver sheet to transfer the film. The portion of the film that has an image thereon is transferred to the final substrate and is mechanically and/or chemically adhered to the final substrate. The cured radiation curable portion of the film renders the non-imaged area of the film non-tacky and non-adhesive, so that it is easily removed from the substrate.